Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 230614
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
114 AM EST TUE DEC 23 2014

.SYNOPSIS...
A MOIST AIRMASS WILL REMAIN ATOP THE REGION BEFORE A COLD FRONT
CROSSES BY WEDNESDAY NIGHT. DRY HIGH PRESSURE WILL ARRIVE FOR
CHRISTMAS DAY AND LINGER INTO FRIDAY. ANOTHER COLD FRONT WILL CROSS
THE AREA ON SATURDAY...FOLLOWED BY HIGH PRESSURE ON SUNDAY.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 1250 AM EST...WATER VAPOR IMAGERY SHOWS A LOW PRESSURE SYSTEM
CLOSING OFF OVER SE NEBRASKA EARLY THIS MORNING. ENERGY PIVOTING
AROUND THE CLOSED SYSTEM TODAY WILL SHARPEN UP THE MAIN TROUGH AXIS
SWD ACROSS THE SRN PLAINS. MEANWHILE...THE LATEST SFC ANALYSIS SHOWS
CONTINUED CAD ACROSS OUR FORECAST AREA...BUT WITH HIGH PRESSURE
WEAKENING SLIGHTLY TO THE N. AS THE UPPER TROUGH CONSOLIDATES TO THE
WEST...ISENTROPIC LIFT OVER THE CAD MAY BRIEFLY WEAKEN THROUGH LATE
MORNING OR EARLY AFTERNOON. HOWEVER...LOW LEVEL MOISTURE AND STEADY
UPGLIDE WILL STILL BE SUFFICIENT FOR HIGH COVERAGE OF LIGHT RAIN OR
DRIZZLE THROUGH THE PERIOD...ALONG WITH AREAS OF FOG WITHIN THE CAD
LAYER AS THE NE FLOW SLOWLY WEAKENS. EXPECT CHILLY TEMPERATURES TO
REMAIN AT LEAST ONE TO TWO CATEGORIES BELOW THE CONSENSUS OF MOS IN
MOST AREAS.

THE MODELS FEATURE EXCELLENT AGREEMENT ON THE SALIENT FEATURES
THROUGH 36 HOURS...WITH THE TROUGH AXIS DEEPENING TONIGHT AS IT
MOVES EWD TOWARD THE MS RIVER VALLEY. AN OPEN GULF AHEAD OF THIS
TROUGH WILL ALLOW MOISTURE TO DEEPEN RAPIDLY TONIGHT...WITH STRONGER
OMEGA RETURNING AS THE 850 MB SRLY JET RAMPS BACK UP. RAINFALL RATES
WILL INCREASE OVERNIGHT AND QPF SHOULD FOCUS MOST STRONGLY IN THE
SRLY UPSLOPE AREAS FROM 06Z TO 12Z. HOWEVER...RAINFALL TOTALS COULD
BE A BIT BELOW MODEL CONSENSUS GIVEN THE EXPECTED GULF COASTAL
CONVECTION. VERY LIMITIED EROSION IN THE SFC WEDGE IS EXPECTED
OVERNIGHT...WITH SLIGHT TEMPERATURE RECOVERY OVER THE FAR SRN/SERN
PIEDMONT SECTIONS LATE. ISOLD ELEVATED CONVECTION SHOULD JUST BECOME
POSSIBLE IN THE EXTREME SRN PIEDMONT TOWARD DAYBREAK WED. FAIRLY LOW
RIVER AND STREAM LEVELS HEADED INTO THE EVENT SHOULD HELP PRECLUDE
HYDRO PROBLEMS WITH ANY HEAVIER RAINFALL LATE TONIGHT.

&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY/...
AT 200 PM EST MONDAY..12Z MODEL RUNS INDICATE THAT SOME SEMBLANCE OF
A WEDGE WILL REMAIN THROUGH MOST IF NOT ALL OF TUE NIGHT. THE NAM
DOES SUGGEST THAT PERHAPS THE SOUTHERN UPSTATE MAY GET UNCOVERED BY
12Z WED. THE UPSHOT FOR TUE NIGHT IS THAT ISENTROPIC LIFT WILL
CONTINUE OVER THE WEDGE WITH WIDESPREAD LIGHT TO EVEN MODERATE RAIN.
BEST RAINFALL RATES ARE EXPECTED TO BE OVER THE WESTERN UPSTATE...NE
GA MOUNTAINS AND THE WESTERN ESCARPMENT WHERE BEST FORCING/UPSLOPE
FLOW WILL BECOME ESTABLISHED. RAINFALL IN THOSE AREAS IS LIKELY TO
BE UPWARDS OF AN INCH. ON WED...THE CONSENSUS IS THAT THE REMAINDER
OF THE WEDGE WILL GRADUALLY BE UNCOVERED...BUT AS USUAL IT COULD
LINGER WELL INTO THE AFTERNOON FROM THE CENTRAL UPSTATE EASTWARD.
RAIN/DRIZZLE WILL BECOME SHOWERY AS WEDGE DISSIPATES. THE NEXT ISSUE
IS THE COLD FRONT THAT WILL TRANSLATE ACROSS THE AREA FROM THE WEST
AS LOW PRESSURE MOVES FROM CENTRAL TN TO THE LOWER GREAT LAKES ON
WED. THE 12Z MODELS ARE TRENDING SLOWER WITH THE FRONTAL PASSAGE...
WITH THE NAM THE SLOWEST OF THE OPERATIONAL RUNS....A GOOD 6 HOURS
SLOWER THAN THE GLOBAL MODELS. THE 09Z SREF SUPPORTS THE SLOWER NAM.
IN REGARD TO TIMING WILL USE A CONSENSUS APPROACH WHICH WILL MOVE
THE FRONT INTO WESTERN SECTIONS DURING WED AFTERNOON AND THEN ACROSS
THE REMAINDER OF THE AREA LATE WED AFTERNOON/EVENING. THE MAIN
CONCERN WITH THE FRONTAL PASSAGE WILL BE THE THREAT FOR SOME SORT OF
QLCS EVENT. ALL THE MODELS SHOW SOME LOW END CAPE UPWARDS OF 200
J/KG AHEAD OF THE FRONT. SHEAR/HELICITY IS ADEQUATE ALTHOUGH NOT
THROUGH THE ROOF BUT FORECAST SHERB VALUES GENERALLY <1.  ALSO...THE
UPPER FORCING IS NOT COINCIDENT WITH THE FRONT. THE UPPER TROUGH IS
FORECAST TO TRAIL THE SURFACE FRONT WITH THE MAIN UPPER FORCING
GOING WELL NORTH OF THE REGION. HENCE...CHANCES FOR SEVERE
CONVECTION APPEAR ON THE LOW END. THE CIPS ANALOG DOES MAKE ME PAUSE
AS IT PAINTS A 30% AREA OF TOP ANALOGS PRODUCING AT LEAST 1 SEVERE
EVENT ACROSS THE PIEDMONTS OF NE GA...SC AND NC. SPC KEEPS THE
MENTION OF SEVERE EAST OF THE AREA...SO BOTTOM LINE IS THAT WE WILL
NOT NOT MENTION THE THREAT OF SEVERE IN THE HWO. DRYER AIR AND
DOWNSLOPING WINDS WILL FINALLY SCOUR CLOUDS OUT EAST OF THE
MOUNTAINS WED NIGHT WITH PERHAPS A PERIOD OF SOME NW FLOW SNOW/RAIN
SHOWERS EARLY CHRISTMAS IN THE MOUNTAINS.

IN REGARD TO HYDRO...I HAVE HEFTY QPF IN MY FORECAST GRIDS WITH
STORM TOTAL RAINFALL AROUND 2.5 INCHES OVER NE GA...WESTERN UPSTATE
AND THE WESTERN ESCARPMENT. HOWEVER...ANTECEDENT CONDITIONS ARE
BENIGN SO DO NOT ANTICIPATE ANY SIGNIFICANT HYDRO CONCERNS.

TEMPERATURES WILL BE A CHALLENGE AS A NON-DIURNAL TREND WILL OCCUR
TUE NIGHT WHERE THE WEDGE ERODES. THIS WOULD MOST LIKELY BE ACROSS
THE SOUTHERN PERIPHEREY OF THE FORECAST AREA. TEMPS ON WED SHOULD
SURGE WELL INTO THE 60S AS THE WEDGE DISSIPATES. COOLER TEMPS WILL
THEN OCCUR WED NIGHT WITH MAX TEMPS THU NEAR CLIMO.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
AS OF 200 PM MONDAY...HIGH PRESSURE OVER THE SRN ATLANTIC REGION WILL
MAKE FOR SETTLED CONDITIONS IN OUR AREA THU NIGHT THRU EARLY
SAT...BEFORE THE HIGH IS FORCED OFFSHORE BY A LONGWAVE TROUGH DIGGING
INTO THE CENTRAL CONUS. GLOBAL MODELS HAVE DELAYED ARRIVAL OF THE
COLD FRONT ON THE LEADING EDGE OF THE TROUGH...NOW SUGGESTING THE
FRONT WILL CROSS THE MTNS DURING THE DAY SAT AT THE EARLIEST.

THE GFS HAS MAINTAINED CONSISTENCY WITH EARLIER RUNS...DEAMPLIFYING
THE TROUGH OVER THE WEEKEND AND ALLOWING DRY HIGH PRESSURE TO FILL IN
ACRS THE SOUTHEAST IN ITS WAKE. EC AND NOW THE OPNL CMC-GEM SHOW A
SIMILAR EVOLUTION ALBEIT MARKEDLY DIFFERENT FROM THE GFS. THEY DEPICT
A SHORTWAVE SHEARING OFF THE TROUGH OVER THE SRN PLAINS SATURDAY
WHICH INDUCES GULF CYCLOGENESIS AND MAKES FOR A WET SUNDAY OVER OUR
CWFA. THIS IS NOT INDICATED BY ANY 22/06Z GEFS MEMBERS AND ONLY A
COUPLE OF THE 22/12Z GEM ENSEMBLE MEMBERS. NOTING HOW DIFFERENT THE
EC/CMC SOLUTION IS FROM EARLIER RUNS IT APPEARS WISE TO DISCOUNT IT
TO SOME DEGREE. LOOKING A BIT FURTHER FORWARD...GFS DOES FEATURE ITS
OWN DIFFERENCES BY LATE MONDAY AS IT SPINS UP A NEW GULF LOW AT THAT
TIME AND BEGINS TO SPREAD PRECIP NWD THRU GA/SC. CONFIDENCE IN THE
FCST IS NOT VERY HIGH BEYOND SATURDAY.

TEMPS SHOULD TREND UPWARD THRU SUNDAY...WITH MINS ENDING UP A COUPLE
DEGREES ABOVE CLIMO AND MAXES 5-7 ABOVE CLIMO. SLIGHTLY COOLER TEMPS
RETURN FOR MONDAY WITH HIGH PRESSURE JUST NORTH OF THE REGION.

&&

.AVIATION /06Z TUESDAY THROUGH SATURDAY/...
AT KCLT...LIGHT UPGLIDE OVER THE PERISISTENT CAD REGIME ALONG WITH
LOW LEVEL MOISTURE WILL BE FAIRLY PERMANENT FEATURES THROUGH THE
TERMINAL FORECAST PERIOD. SOLID LIFR CIGS AND IFR VSBY WILL
RESULT...WITH LIGHT RAIN OR DRIZZLE AT MOST TIMES THROUGH THE
PERIOD. STEADIER RAIN WILL DEVELOP TONIGHT AS A SRLY 850 MB JET
RAMPS BACK UP FROM THE WEST. EXPECT SFC WINDS TO REMAIN NE AT LESS
THAN 10 KT THROUGHOUT.

ELSEWHERE...PERIODS OF LIGHT RAIN AND DRIZZLE WILL CONTINUE IN WEAK
UPGLIDE OVER THE SFC CAD LAYER. IFR CIGS COULD BE A BIT VARIABLE AT
THE START OF THE TERMINAL PERIOD FROM KGSP TO KAVL...BUT CIGS SHOULD
QUICKLY SETTLE DOWN INTO LIFR THROUGHOUT...WITH IFR TO MVFR VSBY
DEPENDING ON THE WINDS. SFC WINDS WILL REMAIN NE LESS THAN 10
KT...EXCEPT SE AT KAVL. STEADIER RAINFALL WILL DEVELOP TOWARD
EVENING AS THE DEEPER MOISTURE AND UPPER SUPPORT ARRIVE FROM THE
WEST. THE IMPROVING SRLY JET WILL ALSO REQUIRE THE MENTION OF LLWS
AT KAVL FOR THE LATTER HALF OF THE PERIOD.

OUTLOOK...DEEP MOISTURE WILL CONTINUE AT ALL TAF SITES UNTIL A COLD
FRONT CROSSES THE AREA FROM THE WEST LATE WED. WIDESPREAD RAIN
SHOWERS AND ASSOCIATED LOW RESTRICTIONS WILL CONTINUE THROUGH FROPA.
DRY HIGH PRESSURE WILL RETURN THROUGH LATE WEEK.

CONFIDENCE TABLE...

            06-12Z        12-18Z        18-24Z        00-06Z
KCLT       MED   75%     MED   70%     MED   70%     HIGH  81%
KGSP       MED   72%     MED   75%     MED   78%     HIGH  90%
KAVL       HIGH  81%     MED   76%     HIGH  85%     HIGH  88%
KHKY       MED   67%     MED   75%     HIGH  83%     HIGH  88%
KGMU       MED   72%     MED   75%     HIGH  81%     HIGH  90%
KAND       MED   75%     MED   73%     MED   78%     HIGH  85%

THE PERCENTAGE REFLECTS THE NUMBER OF GUIDANCE MEMBERS AGREEING
WITH THE SCHEDULED TAF ISSUANCE FLIGHT RULE CATEGORY. COMPLETE HOURLY
EXPERIMENTAL AVIATION FORECAST CONSISTENCY TABLES AND ENSEMBLE FORECASTS
ARE AVAILABLE AT THE FOLLOWING LINK: (MUST BE LOWER CASE)

WWW.WEATHER.GOV/GSP/AVIATION_TABLES

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
NC...NONE.
SC...NONE.

&&

$$
SYNOPSIS...CSH
NEAR TERM...HG
SHORT TERM...LG
LONG TERM...WIMBERLEY
AVIATION...HG



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